Engine and vehicle actuators may be operated via vacuum or electrical energy. Electrical energy may be suitable for operating actuators that require a moderated amount of force; however, vacuum may be more suitable for operating actuators that may require higher levels of force such as vehicle brakes. Vacuum for operating actuators may be supplied via an engine intake manifold or a vacuum pump. An engine may provide vacuum via an intake manifold positioned in the engine air intake path between engine cylinders and an engine throttle. The pumping of engine cylinders may lower pressure in the intake manifold with respect to atmospheric pressure, thereby producing vacuum. However, engine air sources supplying air to the engine may affect the way vacuum is produced by the engine. For example, the engine throttle, engine crankcase ventilation system, EGR, and fuel vapor control system may affect the rate of vacuum production by the engine since the engine throttle and fuel vapor control system supply air to the intake manifold. In addition, the engine throttle and the fuel vapor control system may affect the level of vacuum produced by the engine. Further, choosing between liquid and gaseous fuels in a bi-fuel engine can also affect engine vacuum production. Consequently, if larger diameter hoses are used between vacuum system components to improve vacuum recovery rate of a vacuum system, the engine may not be able to provide vacuum at a desired rate and level.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine operating method, comprising: closing air sources to an engine intake manifold in response to a vacuum level, the air sources including a throttle; evacuating air from an air source supplying air to the engine intake manifold that is not closed; and opening at least one of the closed air sources in response to engine combustion stability degrading below a threshold level.
By restricting air flow or other gases flowing into the engine via closing gas sources capable of providing gas to the engine, the engine can be operated as a vacuum pump to quickly resupply a vacuum system with vacuum. In one example, a throttle supplying air to the engine may be closed in response to a brake booster vacuum level. The throttle may be at least partially reopened in response to a combustion stability level of the engine so that the possibility of engine emission degradation may be reduced during the vacuum recovery period.
The present description may provide several advantages. For example, the approach may reduce the possibility of engine stalls while increasing a rate of engine vacuum production. In addition, some cylinders of a multi-cylinder engine may be operated without fuel to produce vacuum while other cylinders operate with fuel to produce engine torque. Further, the engine may provide higher vacuum levels since the engine throttle can be closed during vacuum production. Further still, engine air sources can be opened in a predetermined order after being closed so as to prioritize operation of vacuum consumers.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.